Treatment of hydrocarbon oils



March 12, 1940. w, GRAY 2,193,625 TREATMENT OF HYDROCARBON OILS Original Filed July 15, 1929 2 Sheets-Sheet 1 INVENTOR- GEO/76E PKG/51y ATTORNEY- March 12, 1940. a. w. GRAY TREATMENT OF HYDROCARBON OILS Original Filed July 15, 1929 2 Sheets-Sheet 2 ADM 7' M ATTORNEY- Patented Mar. 12 1940 UNITED STATES TREATMENT OF HYDROCARBON OILS George W. vGray, New York,

N. Y., assignor, by

mesne assignments, to Texaco .Development. Corporation, New York, N. Y., a corporation of Delaware Original application July 15, 1929,. Serial No;

Continuation of application January 21, 1933, Serial No. 652,786. Divided and this application July '7, 1936, Serial No. 89,422

1 Claim. (Cl.

This application is a division of application Serial No. 378,237, filed July 15, 1929, which has matured into Patent 1,953,013, issued March 27,- 1934, and is a continuation of application S. N. 652,786, filed January 21, 1933, and contemplates an improvement in the treatment of hydrocarbon oils in which oil is subjected to cracking, the products of cracking subjected to distillation to separate out a heavy residue and a vapor fraction, and in which the vapors are fractionated to separate out in addition to a light distillate of the character of gasoline a heavier fraction suitable for further cracking, and an intermediate fraction which is blended with the heavy residue to form a fuel oil of desired test.,

In order to more fully disclose the invention reference will now be had tothe accompanying drawings, wherein Figure 1 is a diagrammatic sectional elevation of an apparatus adapted for the practice of thev invention, I

Figured is an enlarged partial section taken on the line 2-2 of Figure 1.

Figure 3 is an enlarged partial section of the primary distilling chamber showing valve mechanism controlling the transfer of liquid to the secondary distilling chamber.

Figure 4 is an enlarged view side elevation.

Figure 5 is an enlarged view in diagrammatic elevation showing a means for controlling-the passage of vapor from the primary distilling chamber to its fractionating tower.

Referring now more particularly to Figure 1, it will be seen that the apparatus illustrated includes a primary distilling chamber ill in vapor communication with a fractionating tower l l and a secondary distilling chamber l2 in vapor com-' munication with a fractionating tower l3 and arranged to receive the partly distilled residue from the primary still Iii. The oil to be distilled is introduced to the still iii by means of a charging line M which may have a valve it for regulating the admission of oil to the still I0 and also, if necessary, for reducing pressure from that obtaining at the source of supply. The line it may communicate with one or more batteries of cracking converters or stills and is adapted for conducting tar or residue from the cracking stills to the expansion and distilling chamber it.

The charging line it is shown as entering the distilling tower ii! at an intermediate point there in between bail'les ill which are in the form of circular discs suitably secured to the shell of the chamber In and formed with concentric central of this valve in ice-49 openings H, as shown. The line it, as clearly indicated in Figure 2, is arranged, to discharge the oil tangentially into thechamber Hi so as to impart a'whirling movement of the oil adjacent the bafiles Hi. The diameter of each of the 5- openings ll may be the same. However, if the holes be made of different diameters it is ordinarily preferable that the upper opening ll be i the smaller diameter since, if the upper opening be of greater diameter than the'lower open- 10 ing there may be a tendency to decrease the capacity for efficient separation of gas and vapors from the liquid. Underneath the baffle l6 one or more similar bafiles l8 may be provided, as shown in the form of a circular disc having a central opening so as to thus assist in continuing the centrifugal action initiated between the baflies l6. Above the baflles It a plurality of baiiles 2d are disposed in staggered relation, these bafiles being preferably of semi-circular shape" 20 and extending preferably only to the center of the chamber so that platesmounted on opposite sides will not overlap; It may even be preferable under certain conditions to have these baliles extend less than to the center of the 26 chamber, since their primary iunction is to bring about a tortuous path of movement of the vapors and to knockback the liquid particles entrained therewith. This can be done quite effectively without overlapping of the baiiles, which would lid tend to reduce the capacity of the chamber.

The line '2! is arranged to conduct liquid from the primary distilling chamber NJ to the secondary distilling chamber l2. As clearly shown in Figures 3 and 4 the end of the line 2| in the as chamber Ill is connected to a fitting 22 formed with an angular face 25 which constitutes a seat for a flapper v'alve 24. The fitting 22 carries lugs or bosses 25 within which is mounted a pin or shaft 2t which constitutes a pivotal support for 49 the valve 2%. The shaft 26 extends outside the wall of the still it through a stuffing box 21 and carries a lever arm 28 provided with a weight29 which is arranged to normally hold the valveZ l' in open position. The flapper valve 2 carries 45 a paddle or element 30- disposed at an angle to it so that when the valve is open the flow of fluid Wide open position. It is preferable to provide the valve mechanism so that the valve will normally be either in the wide open or fully closed position and so arranged that whenever the force directed against the element 30 is sufflcient to overcome the force of the weight 29 tending to hold the valve open, the valve will thereupon close with an accelerated movement. It will then stay closed until the up-stream pressure falls to within a predetermined difierential in excess of the down-stream pressure. This differential is determined by the size of weight 29, the length of lever arm 23 and the effective area of seat 25.

It is sometimes desirable for flushing purposes to withdraw residue from the lower part of the chamber I 3 in addition to that which is normally discharged through the line 2| and to accomplish this a slotted pipe 35 is shown extending upwardly from the bottom of the distilling chamber I9 and communicating with a drawoff line 32. By having the pipe 3! slotted it is possible to withdraw liquid from the chamber 50 at points above any coke deposits that may collect in the lower end of the chamber. It is advantageous to insert temperature indicating means at different levels in the lower portion of the chamber so as to indicate to the operator the building up of any coke deposits and the desirability of withdrawing liquid through the pipe 3!. The accumulation of coke in the chamber may be indicated by a decrease in temperature at the place where the deposit may occur. Ordinarily it is preferable to make drags through the line 3! at the periods of maximum pressure in the tower I0 which normally is at approximately the end of a drag from the pressure stills through the line I4.

The vapors and gases separated in the tower ID are withdrawn through a vapor line 33. Instead of extending directly to the fractionating tower Ii this line is shown as leading to a heat exchange element 34 for heating the steam supplied to the secondary distilling chamber I2 so as to thus enable the utilization of low temperature or exhaust steam. The vapor line 33 is shown as terminating at the upper end of the chamber 34 which is formed into an upper header by means of a plate 36. A plurality of tubular elements 35 positioned within the chamber extend from the plate 36 to a lower plate 31 which forms a header at the lower end of the chamber. The vapors pass from the upper header through the tubes 35 to the lower header. An exhaust steam line 38 admits steam to the space around the tubes above the plate 3'! while an outlet line 39 is provided for the steam just below the plate 36. The steam in passing through the shell of the exchanger is heated by means of the hot vapors passing downwardly through the tubes of the exchanger and the vapors together with such condensate as is formed enter the pipe 40 by which the vapors and liquid condensate are conducted to the tower II.

To control the passage of Vapor from the distilling chamber Ill to the fractionating tower II and to prevent undue rises in pressure in the fractionating tower the valve mechanism shown in Figure 5 is provided. The valve actuating mechanism includes a leaf or sheet 48 pivoted at 42 and disposed within the pipe 33 in the path of the vapors. The passage of vapor through the pipe'3'3 tends to swing the element 4! on its pivot, it tending tov approach a vertical position or position parallel with the flow of vapor at maximum pressure or vapor flow. The pin 42 extends exteriorly of the pipe 33 and carries a weighted element 43 which tends to hold the element M in the horizontal position or in a position crosswise of the flow of vapors. A lever arm 44 is also secured to the pin 42 and is in operative connection with one arm of a rocker arm 45 by means of a connecting rod 46. The other arm of the rocker arm 45 is connected by rod 47 to a lever 48 arranged to operate a butterfly valve 49 within the pipe 33. When the pressure rises in the still I 0 due to increased influx of material from the line I4 the increased vaporization produces a greater pressure head on the line and increased flow through the line 33 so that the element M is moved toward the vertical position to thus actuate the lever 44, connecting rod 45, rocker arm 45, connecting rod ll and lever 18 to move the valve 49 toward the closed position. In other words the greater the pressure on the leaf 4| or the greater the flow of fluid through the line 33 the greater the tendency for the valve 43 to move to the closed position and thus retard or stop the flow of vapor. The arm carrying the weighted element 43 is preferably placed at such an angle that the restoring force tending to return the leaf 41 to its horizontal position increases as the leaf is forced more and more into the vertical position. As a result of this control mechanism, in spite of wide fluctuations in pressure in the distilling chamber III, the transfer of these violent fluctuations to the tower I I is prevented. While there may be some pressure variation in the tower II the peak pressure loads are topped off so that it is thus possible to obtain in the tower I I distillates of more uniform character throughout a run than could be obtained if the extreme pressure fluctuations which may take place in the chamber ID were permitted to be transferred into the tower II.

The vapor line 40 extends to the bottom of the tower II which is shown formed with a plurality of sections A, B, and C, each of which sections is made up of a plurality of bubble trays 50. A. trap 5I is shown for collecting condensate from the section A and a line 52 extending to a cooling coil 53 is provided for the removal of this cut from the fractionating tower. An outlet pipe 54 extends from the cooling coil 53 to tankage (not shown). A reflux pump is connected to the line 54 and provided with a discharge line 56 so as to pump a portion or all of the condensate to the section B to serve as a reflux therefor.

In order to regulate the quantity of reflux thus returned to the section B, the line 56 will preferably be provided with a pressure-controlled valve 56 so arranged that it will be opened a greater or less extent, depending upon the pres sure at the bottom of the section B. Thus when an increase in pressure occurs at the bottom of section B, due to a greater quantity of vapors being passed to the tower by the line 40, the valve 56 will be opened to a greater extent to permit the introduction of a greater amount of reflux. The pressure-controlled diaphragm for operating the valve 56 may be of conventional construction, although it will preferably be provided with a relatively strong spring so that the extent to which the valve is opened when the pressure increases will depend upon the amount of such pressure. A trap 5'! is provided for receiving condensate from the section B and an outlet line 58 extends to a cooling coil 59 for removing this fraction from the tower. An outlet line 60 extends from the cooling coil 59 to tankage (not shown). A reflux pump BI is connected to the line 60 and provided with a discharge line 62 for introducing as a reflux to the section C a portion or all of the condensate taken off from section B. A pressure-controlled valve 62 will preferably be provided in the line 52 and may be controlled by the pressure at the bottom of the tower H in a manner similar to the control of the valve '6 The final condensate formed in the tower is collected in the bottom and the discharge of this liquid from the tower may be controlled by means of a float83 operatively connected to a valve 64 in an outlet line 65. The outlet line is shown extending to a cooling coil 68 provided with a discharge line 61 extending to tankage (not shown) A vapor line 68 extends from the tower I! to a reflux condenser 89 provided with a reflux condensate line it] for conducting reflux to the upper section A of the tower H. The reflux condenser 69 may be water-cooled or otherwise cooled, as may be desired. The line 56 is shown provided with a branch line 5611 so that if desired a portion of the condensate from the condenser 53 may be admitted as reflux to the upper section A. This branch line may similarly be provided with a pressure-controlled valve regulated by the pressure at the bottom of section A in the same way that the valve 56 is controlled. A vapor line H shown with a pressure regulating valve 12 extends to a condenser coil 13 provided with an outlet line it to a receiver or accumulator drum 15. The pressure regulating valve 12 may be operated in any suitable manner. It may be operated merely by hand, although one advantageous arrangement is to operate the valve 12 by a pressure diaphragm, as shown, controlled by the downstream pressure so that when the pressure in the condenser rises, the valve moves to the closed position to thus reduce or entirely stop the delivery of liquid to the condenser 13. A line H is shown having a valve l6 controlled by the float 19 in the drum E5. The valve 18 may be so operated by the float ldthat when the liquid level is rela tively high no gas is allowed to escape through the line H but with decreased liquid levels gas is permitted to escape. By partially closing the valve in the outlet pipe '55 the flow of gas and naphtha into the receiving drum l5'can be regulated. It should be noted here that due to the admixture of gases with the liquid hydrocarbons rising through the pipe M, the gas lift principle becomes effective to permit placing the drum 15 at a relatively high elevation with a small pressure drop through this pipe. This makes it possible to operate the system under extremely low pressures in the tower ii and drum l5 without requiring a pumpto force the distillate from the drum to tankage.

GUI

If desired, distillate from the line 14 or drum it"; may be pumped to the top of the tower H to serve as a reflux therefor, in addition to or in lieu of the reflux supplied by the run-back line It. A line lilo is indicated for supplying this reflux. which line may extend to a pump (not shown) that may be connected to the line Hi or drum 15.

F A convenient method of regulating the pumping of reflux through the line its to the tower H is to provide automatic means for controlling the rate of pumping in accordance with the pressure obtaining in the tower, just as the valves 56 and are controlled. This automatic means may be arranged to function so that as the pressure increases in the tower the amount of reflux admitted will be increased.

The secondary distilling chamber i2 is shown in the form of a tower provided interiorlywith a plurality of bafiles 8B in the upper portion thereof and a plurality of pans or trays 8| in the lower portion thereof. The line 2!, which introduces residue from the primary distilling chamber ill, is shown entering the tower H at an intermediate point therein so as to discharge liquid onto the pans 8| while the evolved vapors will be obstrucetd in their passage by the bafiles B0. The line 2i may be provided with a check valve 32 so as to prevent the discharge of any fluid from the still i2 back to the still in case the pressure in the still I? should ever rise above that obtaining in the still it. The line 39 is shown entering the lower portion of the tower 2 for introducing steam which has been heated in the heat exchanger 34. i

The withdrawal of residue from the tower is accomplished by a line 83 having a valve 84 controlled by a float B5. The line 83 is shown as being connected to the drag line 32 of the tower is and as extending to a cooling coil 85, the outletoi which extends to a pump 81 for removing the residue to tankage (not shown). A vapor line 88 is provided for removing the vapors to the fractionating tower l3 and the line is shown equipped with a valve 4% actuated by an element Ma for the purpose of retarding the flow of vapor as the pressure in the tower 12 or flow of vapors through the. line 38 increases. The elements Ma and 48a are similar, respectively, to the elements 4! and 49 shown in Figure 5 which have heretofore been described in detail. The employment of the control mechanism Ma and its, while advantageous, is not essential and might well be eliminated.

he tower I3 is shown formed with an upper section D and a lower section E divided by a partition wall 89. The line 88 is shown entering the lower portion of the section D which contains a plurality of bubble trays Bl]. The condensate collected in the section D is removed by a line 9| having a valve 92 controlled by a float 93. The line 9i extends to a cooling coil 94 provided with an outlet line 95 to tankage (not shown) A vapor line 96 is provided .for removing steam together with any oil vapors present and directing the combined vapors into the lower portion of section E which is shown provided with rock or other suitable contact material'il'l. A pipe 98 serves to introduce water to the section E which water may for example be water that has been removed from a condenser box employed in supplying cooling to the coil 13. A line 99 is shown constituting a vent to the atmosphere. the section E together with such oil condensate as may have been formed from any oil vapors present is collected in the bottom of the tower l3 and removed by a pipe Hill to atrap or water leg Hit in which the oil and water are separated, the oil flowing out through a line m2 and thewater being removed by the line N53. The line I82 is shown connected to the line 54, The reflux for the upper section B of the tower i3 is provided by a line Hi l which is shown as a branch line of the reflux line 62 so that condensate from the section B of tower it may be employed as a reflux in the tower l3.' If desired. other condensate such for example as condensate withdrawn from the bottom of the tower i I may well be employed as a reflux to the section D of the tower l3. The discharge line 62 of the reflux pump 6! is shown provided with a branch line I05 connected to the line 83 so that if desired distillate withdrawn from the intermediate section B of the tower it may be mixed with residue ob- Steam that is condensed in v tained from the stills l0 and i2 for the purpose of reducing the viscosity of this residue to such degree as may be desired. Instead of utilizing the condensate from the section B of tower i l for mixing with the still residue any of the other condensates formed in the process may well be employed, such for example as the heavy condensate withdrawn from the bottom of section D of tower I3.

In practicing the invention with the apparatus illustrated liquid oil which has been subjected to a cracking reaction for the conversion of higher boiling hydrocarbons into lower boiling ones, either with or without accompanying distillation, may be admitted through the line M to the primary distilling tower l0. Thus the synthetic product obtained by converting the oil in a vessel from which the vapors are not removed, or the residue resulting from carrying on the cracking with concomitant distillation in a pressure still, is passed through the pressure reducing valve [5 to be thus discharged into the expansion chamber Ii] under reduced pressure. The pressure is reduced to such an extent as is necessary to effect the distillation of the fractions it is desired to remove from the liquid oil or residue. Thus, ordinarily when the conversion is carried on under several hundred pounds pressure, the expansion chamber ill will be held at a pressure considerably reduced from that obtaining in the converters, such for example as pressures approximating atmospheric, and depending upon the exact conditions of delivering the liquid oil or residue from the cracking chambers the pressure in the expansion chamber it] may ordinarily vary for example from approximately atmospheric pressure to 75 or 100 pounds pressure. It is desirable to reduce so far as practicable the pressure obtaining in the expansion chamber but it may be that while pressures approximating atmospheric such as 5 to 10 pounds may be maintained at times, that at other times during periods of heavy drags from the pressure stills the pressure may rise to the upper limits mentioned.

The liquid oil is discharged into the chamber H? in a stream tangential to the wall of the chamber, as has been pointed out, so as to impart a whirling motion to the liquid between the concentric central hole baflles i6 thus facilitating the separation of the gas and vapors from the liquid residue. By discharging the oil tangentially into the chamber at a rapid rate a centrifugal force of sufficient magnitude to materially increase the separating efiect over that which would otherwise take place may be accomplished. As an indication of the separating force which has been obtained in the practice of the invention it may be mentioned that in some operations carried on in accordance with the invention a separating force calculated as upwards of 770 times the force of gravity has een employed. In addition to the separating action carried on in the whirling mass of oil between the central hole baffles there is a further separation in the upper portion of the chamber 10. Thus the separating action that takes place in the still l0 may be referred to as a two-stage operation, the first of which is carried on at relatively high speed in which separation of the vapors from liquid takes place under the influence of centrifugal action and the second stage of which takes place in the upper part of the still l0 where the vapors travel at reduced velocity through the baffled portion of the chamber wherein any solid particles of suspended coke or carbon or heavy entrained liquids are separated out from the vapors by reason of the obstructing baflles and reduced velocity.

The vapors pass from still I 0 through the vapor line 33 to the exchanger 34 and thence through the line 40 to the fractionating tower i i wherein fractionation of the vapors takes place. Liquid residue is discharged into the secondary distilling chamber l2 into which steam which has been heated by heat exchange with the hot vapors from the expansion chamber I0 is introduced. The delivery of liquid or residue from the primary still in to the secondary still !2 is retarded, as has heretofore been explained, by the operation of the valve 24 in the line 2| so that undue rises in pressure in the primary still I 0 or a heavy influx of material through the line into the still ID will not overload the secondary still !2 or cause the pressure to rise therein unduly. The delivery of vapors from the primary still It to its fractionating tower H is also retarded by the operation of the valve 49 in the line 33, as has heretofore been explained, so as to reduce the effect in the tower ii of periods of high pressure or of increased evolution of vapor in the still I0.

In the fractionating equipment shown an overhead vapor fraction and three condensate cuts may be taken off the fractionating tower ll. Thus a gasoline or naphtha fraction may be taken oif through the line 68, passed through the reflux condenser 59 and line H to the condenser coil 73, the distillate being collected in the receiver l5. Fractions constituting kerosene or light or intermediate gas oil fractions may be removed from the tower through the lines 52 and 58. These cuts may be sent to separate storage or, if desired, a portion or all of these fractions may be employed in refluxing towers ii and I3, as has heretofore been explained. A heavier gas oil fraction may be withdrawn from the tower H through the line 65. The tower l3 in which are treated the vapors from the secondary still Ii! is preferably operated so that a heavy gas oil fraction may be drawn off from the bottom of the section D through the line 9!. It is preferable to maintain such temperatures in the section D that the steam which comes oil from the still I? together with the oil vapors through the line 88 will not be condensed and thus the steam together with the hydrocarbon constituents that remain in the vapor form under the temperatures obtaining in the section D pass out through the line 95 to the lower section E of the tower l3. Water is admitted to the contact material 91 to eifect condensation of both the steam and the hydrocarbon vapors. the condensate being delivered through the line 500 to the water leg Hill in which separation of the oil and water takes place.

The distillation system described herein may be employed in distilling liquid oil or residue obtained from a single converter or battery of converters or it may be operated in conjunction with a plurality of converters or batteries thereof. By connecting the line M to a plurality of converters or batteries of converters and by properly timing the intervals between the taking of shots or drags it is possible to reduce to a greater or less extent, depending upon the number of batteries thus connected, the fluctuations in pressure and in volume of liquid obtaining in the primary still l0. But the invention described herein is well adapted for operation under conditions wherein extremely wide fluctuations in pressure and in volume of liquid delivered to the primary still may take place. In some cases instead of taking shots or drags from the converters the removal of liquid or residue may be made in a substantially continuous manner andin this type of operation the invention is of advantage since a continuous stream of liquid may be discharged tangentially into the chamber i between the concentric central hole baffles 1'6 and the separation of vapors and gasesfrom liquid residue carried on in an effective manner.

The gas oil cuts or fractions that are removed from the fractionating towers H and i3 may advantageously 'be returned to the cracking stills or converters for further treatment. It is advantageous to return these reflux condensates to the converters in a heated condition and when it is desired to operate in this manner the cooling coils employed in cooling these condensates may be omitted or the coils may be employed only for cooling such portions of the condensates as it is desired to return to the towers to. serve as reflux media therefor, the other portions of the, condensates being conducted directly to a'cracking zone for further treatment for the production of gasoline.

In order to obtain the maximum production of gas oil (often referred to as cycle gas oil) adapted for returning to the cracking zone for retreatment it is desirable to carry on the distillation of the pressure tar to such an extent that the resultant residue may have a higher viscosity or a lower A. -P.. I. gravity than may be required for a marketable fuel oil. In such case the heavy residue may be-cut with a portion of the gas oil obtained from the distillation. One of the methods of operation contemplated by the invention consists in utilizing the heavier gas oil obtained 7 for return to the cracking zone and employing a the cracking zone but are utilized in the preparation of the desired fuel oil while the heavier and less refractory gas oil'fractions are employed in further cracking for the production of gasoline.

When using steam in distilling the pressure tar either in a single distilling chamber or when carrying on the distillation in'two stages, such as,

has been described as applicable to stills Hi and I2 with the introduction of steam into thesecondary distilling chamber 12, it has been found that when it is desired to obtain a residue to be used for fuel purposes it is satisfactory to use comparatively low temperature steam. and when it isdesired to obtain an asphalt best results are obtained by employing higher temperature steam.

In one method of operation contemplated by the invention oil which it is desired to distill or strip is heated to the desired distilling temperature in a tubular heater and then discharged into the still iii tangentially of the chamber between the concentric central hole baifies it to thus accomplish an effective separation of the vapors from the liquid residue. 'This method of operation may be applied'to a cracking process." Thus the oil to be converted may be raised toa cracking temperature in a coil or tubular heater under high superatmospheric pressure and cracked-to the extent desired and then discharged into the still l0 which may beheld at high superatmospheric pressure or at a pressure materially reduced from that obtaining in the coil. Separation of the vapors from the liquid is facilitated by discharging the oil from the coil into the still Iii tangentially and between the central hole' baffles 16. r

In describing herein the method of employing the still 10 no reference has been made to the application of heat to the still I!) other than that contained in the oil discharged thereinto for distillation because the operation carried on in this type of still is particularly adapted for carrying on distillation o-f oil which is received from a heated source, such as for example acoilor tubular heater or a heated body of oil from a cracking still, wherein the oil contains sufficient-heat for effecting the desired vaporization'when discharged into the still l9. However, it is to be understood that the application of heat to the still ID, or the use of a carrier gas-"such, assteam; is not precluded in the practice of the invention. However, one of the specific methods of operation contemplated by our invention consists in carrying on a distillation in a two-stage operation, such ashas been described as obtaining in the stills i0 and [2 in which, no heat need be applied to the still [0, the distillation being carried of either heat or a carrier gas in the'secondary w distilling operation carried on in the still l2.

Although the preferred embodiment. of theinvention has been set forth in connection with apparatus having 'a particular construction and arrangement of parts and mode of operationyit is obvious that various changes andmodifications may be made therein, while securing to a greater 7 or less extent some or all of the benefits of the lnvention, without departing from the spirit and scope thereof. Therefore, onlysuch limitations should be imposed as 'areindicated in'the appended claim.

I claim:

In the treatment of hydrocarbon oils, the process that comprises passing residual products with. drawn from a pressure cracking still into a flashing zone wherein the residual products are subvjected to flash vaporization to produce heavy residue, subjecting resultant separated vapors to fractionation in a separate fractionating zone-to form a gasoline fraction and higher boiling con densates comprising light gas oil and heavy gas oil condensates, subjecting heavy residue from said flashing zone to further distillation in a secondary flashing zone to form aheavy residue having a viscosity greater than that adapted for fuel oil and produce additional heavy gas oil condensate, subjecting said heavy gas oil condensates to cracking, withdrawing said heavy residue from the secondary flashing zone and conducting it to a blending zone, blending said heavy residue therein with light gas oil condensate withdrawn 

